Method of shaving shoulder gears



Oct. 11, 1949. D; D. AUSTIN, SR 2,484,432

METHOD OF SHAVING SHOULDER GEARS Filed April 14, 1947 i/ 2o 7 V 25 4 l2 1o Z TA l1:\

I I l/ l3 1 14 $1 INVENTOR.

D ON-ALD D. AUSTIN SR.

BY Wm, M Y ATTORNEYS Patented Oct. 11, 1949 UNITED STATES PATENT OFFICE Donald D. Austin, Sr., Detroit, Mich, assignor to National Broach 8r Machine Company, Detroit, Mich., a corporation of Michigan 4 Application April 14, 1947, Serial No. '141,336

(c1. SO-1.6.)

- 2 Claims. 1

The present invention relates to a method of shaving shouldergears.

The finishing of gears to accurate dimensions by a method of crossed axes shaving has come into wide usage but it has been subject to certain :limitations insofar :as the final finishing of shoulder gears is concerned. By the term shoulder gear is meant a smaller one of a cluster of gears on the same shaft, the gears being of different diameter, or a gear next to a part of larger diameter on the same shaft, IZhis leads to a problem of interference when attempting to shave agear of relatively small diameter which is closely spaced from a gear or other partof. larger diameter.

In the past, shoulder gears have been shaved by various modifications-of the crossed axes shaving process, one of such methods being described in the patent to Mentley, 2,411,973, granted December 3, 1946.

It is found that if a gear and gear-like cutter are rotated in mesh atcrossed axes and if a relative traverse between :the gear and cutter is effected, the direction of which occupies a lane parallel to the axes of bothigear and cutter and which direction is oblique to the axes of both gear and cutter, a superior shaving operation may be carried outon shoulder gears.

It is accordingly an object of the present invention to provide a new method'of shaving shoulder gears characterized :by the ability to shave gears of small diameter closer to larger gears without encountering interference between the cutter and the larger gear.

It is a further object of the present invention to provide a new method of shaving shoulder gears in which a smaller crossed axes relationship may be employed, thus reducing'the effect :of interferenoe limitations.

More specifically, it is a featured the present invention to shave a shoulder gear with a rotary shaving cutter by a method which comprises "selecting a crossed taxes relationship limited by minimum clearance conditions, meshing the gear and cutter at such crossed axes relationship, rotating said gear and cutter mesh,'and effecting a relative traverse between the gear and cutter a plane which is parallel to the axes of both gear and cutter and in a'dlrection oblique to 'theaxes of both gear and cutter; which direction occupies an acute angular zone in said plane delimited by the projection in said plane or the axis of said gear on one side and theed'ge-of said cutter on the other side. I

Other objects and features :of the invention will become apparent asthe description proceeds,

especially when considered in conjunction with the accompanying drawing, wherein:

The single figure is a diagrammatic view illustrating the meshed relationship between a cutter and shoulder gear in accordance with the present invention.

Referring now to the figure, there is illustrated at II] .a shoulder gearcomprising a relatively large gear H and a relatively small shoulder gear [2 which is to [be machined eby acrossed axes shaving operation. The axis of the cluster gear II is indicated at 1-3.

Inlorder to finish the teeth of the shoulder gear H completely across thelength thereof and particularly .to the ends thereof adjacent the larger gear H, it 'isnecessary for a cutter 2D to reach a limiting position indicated by dotted lines 20', at which time the axis 2| of the cutter occupies a position '21 and lcrosseswith the axis I3 of the shoulder gear 12 :at a point designated C. It will be observed that the inner edge 22 of the cutter 'at this time is in the position 22' closely adjacenttola corner'of the larger gear I I. In the figure, theedge 211s shown diagrammatically as apparently contacting the corner of the larger gear H, but .it will be appreciated that in fact the cutter 20 and gear H are in different vertical planes so that the-condition illustrated does not represent actual interference between the cutter and the larger gear :1 L Assuming, however, that .the dotted line position of the cutter 20 illustrates the limiting condition from minimum clearance considerations, it will be appreciated that this same condition determines the maximum crossed taxes setting which may be employed.

In the diagram, the angle of crossed axes is illustrated ason theorder oi .159. This is anexaggeration :of the angular relationship between the axes of the gear andcutter which has been made for the vPrimrose of clarifying the diagram. In practice it is .ioundlthat the axes :may be crossed at very small tangles down-to angles of 2 when thepresent method is employed.

In order to iobtain the hill benefit of the present shaving operation it-isnecessarythat the cutter and gear have a relative traverse in a direction which is oblique to the axes of'both gear and cutter :and which traverse .further is in a direction whichoecupies'the angular zone Z 'delimitedrby the axis 18 fOfiZhe :g'ear onone side and the edgefl of the mutter 211 the other side.

Incrossed axes shaving theoretical contact between the teeth or "the gear andthe teeth of the cutteris located ea smail zone which is detersuggested in the past. traverse is perpendicular to the axis of the gear.

. 3 mined by the instantaneous common normal to the axes of the gear and cutter, this zon being known in the art as the center of crossed axes. In order to distribute the finishing action of the shaving cutter across the teeth of the gear from one end thereof to the other, it is necessary to introduce a relative traverse b-etweenthe gear and cutter, this trverseoccupying a plane which is parallel to the axes of the gear and cutter and which may be in a number of different directions in such plane. the gear and cutter is in a direction parallel to the axis of the gear, the center of crossed axes remains fixed with respect, to a definite zone of the cutter, thus causing excessive wear in the cutting zone without employing the full Width 'of the cutter. On the other hand,- if the relative traverse were in a direction parallel to the axis of the cutter, the center of crossed axes would remain fixed with respect to a definite zone on the gear and accordingly the teeth of the gear would not be machined uniformly from end to end. Instead, they would be provided with a hollow whose maximum depth coincided with the zone determined by the center of crossed axes.

Other directions of relative traverse have been One such direction of This direction of traverse has the disadvantage that it tends to reproduce marks on the teeth of the gear corresponding to the cutting edges provided on the teeth of the cutter. In my prior copending application, Serial No. 694,477, filed September 3, 1946, there is suggested the possibility of efiecting relative traverse in a direction oblique to the axes of both gear and cutter, which direction forms an angle of not more than 65 with the axis of the cutter. This traverse, which is termed diagonal traverse, has certain definite advantages. Among these, it causes the center of crossed axes to shift simultaneously with respect both to the gear and the cutter, thus extending the finishing action of the cutter uniformly across the length of the gear teeth from one end to the other andalso distributing the wear longitudinally across the width of the cutter.

Referring again to Figure l, considering the two limiting sides of the angular zone Z separately, it will be appreciated that relative traverse in the direction of the axis [3 of the gear is what has come to be known as conventional shaving. Traverse in this direction results in the center of crossed axes remaining fixed with respect to the cutter so that in order for the cutter to machine the inner ends of the teeth of the smaller or shoulder gear I2, the initial set-up must be such that the center of crossed axes is at the left-hand edge of the cutter at all times. This requires the stroke or traverse to be relatively long and further leads to undesirable unbalanced conditions. These conditions may be overcome in part by imposing a corrective angular displacement of the cutter relative to the gear as disclosed in the patent identified above, but if I possible it would be preferable to avoid the necessity for imposing such corrective angular displacement.

The other boundary of' the angular zone Z is determined by the side 23 of the cutter 20. If'

traverse were in the direction of the side 23, or perpendicular to the cutter axis, the result would be the formation of cutter marks on the teeth of the gear which would not be wiped out and which would render the gear unacceptable to the indus- If the relative traverse between try. However, if the direction of traverse is oblique to the axis l3 of the gear and the side 23 of the cutter and occupies the zone Z, by a judicious selection of the precise angle of traverse it is possible to avoid the necessity for excessive traverse, the corrective angular displacement between the gear and cutter, and the formation of undesirable cutter marks on the teeth of the gear. The direction of traverse may be varied substantially so long as it does not approach too closely to a direction parallel to the axis It of the gear on the side 23 of the cutter, and further so long as it does not exceed an angle of 65 with respect to the cutter axis, as fully set forth in my prior .copending application, identified above.

In the diagram of Figure 1, the direction of traverse is illustrated as parallel to the lines 30,

'moves to the dotted line position indicated at 2!, at which time the center of crossed axes C has shifted to the opposite side of the cutter and to the side of the gear [2 which is closer to the larger gear II. This means that the finishing action has been distributed uniformly from one end to the other of the gear teeth and at the same time the cutting action has been performed by the entire length of the cutter teeth.

In the diagram the width of the cutter 20 is illustrated as just sufficient to finish the width of the gear [2, although in practice it may be somewhat wider if desired. It will further be appreciated that the theoretical width of cutter necessary to finish a definite width of gear varies in accordance with the traverse angle selected. In the illustrated diagram the traverse angle TA, which is the angle between the direction of traverse and the axis of the gear, is illustrated as about 40.

- In prior conventional shaving, that is, crossed axes shaving in which the direction of relative traverse is parallel to the axis of the gear, the minimum crossed axes setting has been said to be about 3". However, in practice it is found that at angles less than about 6 the cutting action has not been entirely satisfactory and instead of removing metal in a free cutting operation there has been a tendency for the cutter to burnish the teeth of the gear. When employing the present method of shaving shoulder gears, a crossed axes setting of as low as? has been employed and the cutting action has been observed to be exceedingly'free and accurate. The reason for this free cutting employing the diagonal traverse disclosed herein is not entirely clear from a theoretical point of View, but it has been amply demonstrated in practice.

It is thus possible by employing diagonal traverse to reduce the crossed axes setting to an angle much smaller than previously thought practical, thereby making it possible to shave shoulder gears in which the smaller gear being shaved is closer to the adjacent larger gear than has previously been possible. a

It may be pointed out that one of the objections to finishing a shoulder gear with the conventional process which involves relative traverse in a direction parallel to the axis of the gear is that all of the cutting done by the cutter is performed by the ends of the cutter teeth. When the present invention is practiced the cutting action is initiated at one end of the cutter teeth and terminates at the opposite end thereof so that at no time is end cutting by the cutter teeth being performed.

Having in mind the fact that the traverse angle employed in diagonal traverse crossed axes shaving should be less than 65 (as disclosed in my prior copending application) and since the present method involves a relatively small crossed axes setting, it will be understood that the traverse direction will in all cases be between a direction parallel to the axis of the work, and a direction making an angle of not more than 65 with the cutter axis. However, traverse angles of less than about to the work axis are so closely equivalent to conventional traverse parallel to the axis of the gear that in order to obtain the benefits of the present method the traverse angle should be greater than 5. As a result, it is possible to define the traverse direction as a direction between a direction parallel to the axis of the work, and a direction making an angle of not more than 65 with the cutter axis.

Inasmuch as the dotted line position of the cutter represents the limiting condition under which the teeth of the gear l2 have been machined from end to end, it is necessary for the first traverse of the cutter to be toward the larger gear of the cluster, or in other words the first traverse must correspond to a movement of the cutter 20 from the full line position to the dotted line position 20'. Normally the machining operation will include a reverse stroke during which the cutter moves relative to the gear from the dotted line position 20' to or beyond the full line position.

If the direction of traverse between the gear and cutter were in a direction perpendicular to the axis of the gear, the dotted line position 20' of the cutter would represent the positions of the gear and cutter at the beginning rather than the completion of a cutting stroke. In other words, to employ relative traverse in a direction perpendicular to the axis of the gear Would necessitate a smaller crossed axes setting to avoid interference between the cutter and the corner of the larger gear ll. Stated differently, the present method of diagonal traverse crossed axes shaving of shoulder gears permits the employment of larger crossed axes.

Where the direction of traverse has been referred to in the foregoing, and where it is recited in the claims, it is to be understood that this is a basic relative traverse which may if desired be modified by superimposing thereon additional relative motions, such for example as a relative rocking motion for producing crowned or otherwise modified gears. In such cases the relative traverse defined may then be merely a major component of a compound relative movement made up of two or more components.

While there is diagrammatically illustrated and fully described a specific method of shaving shoulder gears by diagonal traverse crossed axes gear shaving, it will be understood that this specific disclosure is made solely to enable those skilled in the art to practice the invention, the scope of which is indicated by the appended claims.

What I claim as my invention is:

l. The method of shaving shoulder gears with a rotary gear-like cutter which comprises selecting a crossed axes setting determined by minimum clearance conditions when the common normal to the axes of the gear and cutter is adjacent the edges of the gear and cutter which are next to the shoulder of the gear, meshing the gear and cutter at such crossed axes setting with the common normal to the axes of the gear and cutter located adjacent the edge of the gear remote from its shoulder and with said common normal remote from the edge of the cutter next to the shoulder of the gear, rotating the gear and cutter in mesh, and effecting a slow relative traverse between the gear and cutter which occupies a plane parallel to the axes of both gear and cutter and which occupies the acute sector in the plane located between the axis of the gear and the side of the cutter, the direction and length of the traverse stroke being related to the crossed axes setting such that at the end of the stroke the common normal to the axes of the gear and cutter are closely adjacent the edges of the cutter and gear which are next to the shoulder of the gear.

2. The method of shaving shoulder gears with a rotary gear-like cutter which comprises selecting a crossed axes setting determined by minimum clearance conditions when the common normal to the axes of the gear and cutter is adjacent the edges of the gear and cutter which are next to the shoulder of the gear, meshing the gear and cutter at such crossed axes setting with the common normal to the axes of the gear and cutter located adjacent the edge of the gear remote from its shoulder and with said common normal remote from the edge of the cutter next to the shoulder of the gear, rotating the gear and cutter in mesh, and efiecting a slow relative traverse between the gear and cutter which occupies a plane parallel to the axes of both gear and cutter and which occupies the acute sector in the.

plane located between the axis of the gear and the side of the cutter, the direction and length of the traverse stroke being related to the crossed axes setting such that at the end of the stroke the common normal to the axes of the gear and cutter are closely adjacent the edges of the cutter and gear which are next to the shoulder of the gear and thereafter reversing the relative traverse stroke to bring the gear and cutter to initial relative position.

DONALD D. AUSTIN, SR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,270,422 Drummond Jan. 20, 1942 2,344,292 Drader Mar. 14, 1944 2,380,261 Praeg July 10, 1945 2,411,973 Mentley Dec. 3, 1946 FOREIGN PATENTS Number Country Date 480,247 Great Britain Feb. 14, 1938 

